JP2009187020A - Image forming apparatus - Google Patents

Abstract

Regardless of the type of recording material and the state of a fixing device before the start of printing, control parameters relating to fixing are appropriately corrected, thereby stabilizing the fixing quality.
A first temperature detection element 30 for detecting the temperature of a pressure member 26, a second temperature detection element 28 for detecting the temperature of a recording material that has passed through a pressure nip (N), and The first temperature detected by the first temperature detecting element 30 at the start of the printing operation and the second temperature detecting element 28 when the first recording material passes through the press-contact nip (N). And a correction unit 27 that corrects a control parameter (for example, a fixing temperature) related to the subsequent fixing of the second recording material based on the second temperature.
[Selection] Figure 2

Description

  The present invention relates to an image forming apparatus having a heat fixing unit for fixing a toner image formed on a recording material.

  2. Description of the Related Art Conventionally, many electrophotographic copying machines, printers, and the like employ a contact heating type heat roller fixing method and an energy saving type film heating method, which have good thermal efficiency and safety, as a heat fixing means.

  As shown in FIG. 6, the heat fixing device of the heat roller fixing method includes a heating roller (fixing roller) 62 as a heating rotator containing a halogen heater 61 therein, and a pressure rotator pressed against the heating roller. The pressure roller 63 is a basic configuration. The pair of rollers is rotated, and a recording material (transfer material sheet / electrostatic recording material) as a heated material in which an unfixed image (toner image) is formed and supported in a fixing nip portion that is a pressure nip portion of the pair of rollers (Electrofax paper, printing paper, etc.) 64 is introduced, and is nipped and conveyed to fix the toner image as a permanently fixed image on the recording material surface by heat from the fixing roller 62 and pressure applied to the fixing nip. Is.

  On the other hand, film heating type heat fixing devices include, for example, JP-A-63-313182 (Patent Document 1), JP-A-2-157878 (Patent Document 2), and JP-A-4-44075 (Patent Document 3). ), As proposed in JP-A-4-204980 (Patent Document 4), etc., a heat-resistant film (rotating body for heating) Hereinafter, a fixing nip is formed by a heating member and a pressure roller, with the fixing film sandwiched between the fixing film and a rotating pressure member (hereinafter referred to as a pressure roller) and then slidingly rotated. The recording material carrying the toner image is introduced into the fixing nip portion, conveyed together with the fixing film, and the toner is applied by the heat from the heating body applied through the fixing film and the pressing force of the fixing nip portion. It is intended to heat and pressure applied as a permanent fixed image an image on a recording material surface.

  A film heating type heat fixing device can use a low heat capacity linear heating element such as a ceramic heater as a heating element, and a thin film having a low heat capacity as a fixing film, thereby reducing power consumption and shortening the wait time. Start) is possible. In addition, a film heating type heat fixing device is a fixing film driving method in which a driving roller is provided on the inner surface of the fixing film, or a method in which a pressure roller is used as a driving roller and a fixing film is driven by a frictional force with the pressure roller. (Pressure roller driving system) is known, but in recent years, a pressure roller driving system having a low number of parts and a low cost is often used.

  In the heat fixing apparatus as described above, it is known that the fixability of the toner image on the recording material is greatly influenced by the surface property of the recording material. In particular, in the case of a paper type (hereinafter, rough paper) such as bond paper or raid paper having rough surface properties, the fixability is remarkably impaired. This is because a contact area between the heating member and the recording material is reduced in the fixing nip portion, so that a sufficient amount of heat is not supplied to the toner on the recording material.

  In order to obtain good fixability even on rough paper, it is necessary to increase the fixing pressure or the fixing temperature. In the method of increasing the fixing pressure, the driving torque of the heat fixing device is also increased, so that the image forming apparatus is large and the cost is often increased. As a result, in order to satisfy the fixing property even on rough paper, a method of increasing the fixing temperature must be adopted.

  However, if the fixing temperature is simply increased, an excessive amount of heat is supplied to the toner on the recording material for recording materials such as thin paper and smooth paper (hereinafter referred to as smooth paper). In other words, there may be adverse effects such as occurrence of hot offset and deterioration of the curl of the recording material.

  In this way, the optimum fixing temperature differs between rough paper and smooth paper, and it has been very difficult to achieve both at one fixing temperature. Conventionally, the user can arbitrarily set the fixing temperature (fixing mode) according to the recording material. The correspondence that can be selected was taken. However, it is difficult for the user to select the fixing mode with a parameter that is difficult to understand, such as the roughness of the surface of the recording material, and it has been desired to automatically switch to the optimum fixing mode according to the recording material.

  One method is to detect the temperature of the recording material that has passed through the fixing nip of the heat fixing device (hereinafter referred to as the paper discharge temperature) and feed it back to the fixing control, that is, fixing so that the amount of heat applied to the recording material is kept constant. For example, JP-A-1-150185 (Patent Document 5) and JP-A-7-230231 (Patent Document 6) can stabilize the fixing property regardless of the type of recording material by correcting the temperature. Has been proposed.

JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-204980 JP-A-1-150185 Japanese Patent Laid-Open No. 7-230231 (FIG. 4)

  However, if the control parameter (for example, the fixing temperature) related to fixing is corrected only by the information on the paper discharge temperature, a fixing failure may occur by mistake.

  That is, when a standby fixing device is used to start continuous printing at a fixed fixing temperature and the discharge temperature is measured, the first sheet is the highest, but the second and subsequent sheets are abruptly lowered, and 10 There is a tendency that it gradually starts to rise from the vicinity of the first sheet and converges to a predetermined temperature. However, when the state of the fixing device before continuous printing is high due to intermittent printing or the like, it is common that the first sheet is the highest, but for example, the second sheet and thereafter gradually decrease. When the temperature is converged to a certain temperature as it is, or slightly lower after the second sheet, but gradually rises from the vicinity of the fifth sheet and converges to a certain temperature, a difference occurs depending on the warming condition of the fixing device. End up. That is, the transition of the discharge temperature during continuous printing differs depending on the state of the fixing device before printing, and the discharge temperature at the same number of sheets does not necessarily match. Therefore, a fixing failure may occur due to incorrect correction of the fixing temperature. It is.

  The variation in the discharge temperature transition is largely caused by the state of the fixing device before printing, that is, the difference in the surface temperature of the pressure roller and the heat storage amount. In particular, since the above-mentioned film heating type heat fixing device has the heater turned off during standby, the pressure roller state is not kept constant as in the above-described heat roller type, and pressure is applied during printing. Since the change amount of the roller temperature is large, there is a tendency that the variation of the discharge temperature transition becomes larger.

  The present invention solves the above-mentioned problems, and the object of the present invention is to appropriately correct the control parameters related to fixing regardless of the type of recording material and the state of the fixing device, thereby stabilizing the fixing quality. There is to make it.

  According to one aspect of the present invention, an image forming unit that forms an unfixed toner image on a recording material, an endless belt, a heater that contacts an inner surface of the endless belt, and the fixing nip together with the heater via the endless belt. A pressure roller that forms a portion, and a heating fixing portion that heats and fixes an unfixed toner image on a recording material by sandwiching and conveying a recording material carrying an unfixed toner image at the fixing nip portion, A temperature detection element that detects the temperature of the recording material that has passed through the fixing nip, and a detection parameter of the temperature detection element and a threshold value are compared to correct a control parameter relating to fixing of the recording material that carries an unfixed toner image. The threshold value is set according to the temperature of the pressure roller when the print signal is received in a standby state waiting for the print signal. When the print signal is received in the standby state and printing is continuously performed on a plurality of recording materials, the correction means includes the threshold value set according to the temperature of the pressure roller, and the fixing A control parameter relating to the fixing of the subsequent second recording material in continuous printing by comparing the temperature of the first recording material that has been heated and fixed in the nip portion and passed through the fixing nip portion with the temperature detection element. There is provided an image forming apparatus characterized by correcting the above.

  According to the present invention, regardless of the type of recording material and the state of the fixing device, control parameters relating to fixing are corrected appropriately, thereby stabilizing the fixing quality.

1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to a first embodiment of the present invention. 1 is a cross-sectional view illustrating a configuration of a heat fixing device according to a first embodiment of the present invention. It is sectional drawing which shows the structure of the modification of the heat fixing apparatus in the 1st Embodiment of this invention. It is sectional drawing which shows the structure of the heat fixing apparatus in the 2nd Embodiment of this invention. FIG. 10 is a diagram illustrating an example of a threshold value for determining a correction content of a fixing temperature in the second embodiment of the present invention. It is sectional drawing of the heat fixing apparatus in a prior art example. It is a figure explaining correction | amendment of the fixing temperature in the 1st Embodiment of this invention. It is a figure explaining the correction | amendment of the conventional fixing temperature. It is a figure which shows the result of the experiment for confirming the effect of the 1st Embodiment of this invention. It is a figure which shows an example of the table referred in order to determine the correction content of the fixing temperature in the 2nd Embodiment of this invention. It is a figure which shows the result of the experiment for confirming the effect of the 2nd Embodiment of this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

<First Embodiment>
[1. Image forming apparatus M]
FIG. 1 shows an image forming apparatus according to an embodiment of the present invention, that is, an image forming apparatus provided with a heat fixing device to which the present invention is applied. FIG. 1 is a longitudinal sectional view showing a schematic configuration of a laser beam printer as an example of an image forming apparatus according to the present invention.

  First, the configuration of a laser beam printer (hereinafter referred to as an image forming apparatus) will be described with reference to FIG.

  The image forming apparatus shown in FIG. 1 includes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier. The photosensitive drum 1 is rotatably supported by the apparatus main body M, and is rotationally driven at a predetermined process speed in the direction of arrow R1 by a driving unit (not shown). Around the photosensitive drum 1, a charging roller (charging device) 2, an exposure device 3, a developing device 4, a transfer roller (transfer device) 5, and a cleaning device 6 are arranged almost in order along the rotation direction. . A sheet feeding cassette 7 that stores a sheet-like recording material P such as paper is disposed below the apparatus main body M, and the sheet feeding roller 15 is sequentially arranged from the upstream side along the conveyance path of the recording material P. A transport roller 8, a top sensor 9, a transport guide 10, a heat fixing device 11, a paper discharge sensor 29, a transport roller 12, a paper discharge roller 13, and a paper discharge tray 14 are arranged.

  Next, the operation of the image forming apparatus having the above configuration will be described. The photosensitive drum 1 that is rotationally driven in the direction of arrow R1 by a driving means (not shown) is uniformly charged to a predetermined polarity and a predetermined potential by a charging roller 2.

  The charged photosensitive drum 1 is subjected to image exposure L based on the image information by the exposure device 3 such as a laser optical system on the surface, and the charge of the exposed portion is removed to form an electrostatic latent image.

  The electrostatic latent image is developed by the developing device 4. The developing device 4 includes a developing roller 4a. A developing bias is applied to the developing roller 4a to attach toner to the electrostatic latent image on the photosensitive drum 1 and develop (develop) it as a toner image. The toner image is transferred to the recording material P such as paper by the transfer roller 5.

  The recording material P is stored in the paper feed cassette 7, fed by the paper feed roller 15, transported by the transport roller 8, and transferred between the photosensitive drum 1 and the transfer roller 5 via the top sensor 9. It is conveyed to the nip part. At this time, the leading edge of the recording material P is detected by the top sensor 9 and is synchronized with the toner image on the photosensitive drum 1. A transfer bias is applied to the transfer roller 5, whereby the toner image on the photosensitive drum 1 is transferred to a predetermined position on the recording material P.

  The recording material P carrying the unfixed toner image on the surface by the transfer is transported to the heat fixing device 11 along the transport guide 10, where the unfixed toner image is heated and pressurized and fixed on the surface of the recording material P. The The heat fixing device 11 will be described in detail later.

  The recording material P after the toner image is fixed is transported by the transport roller 12 and discharged onto the paper discharge tray 14 on the upper surface of the apparatus main body M by the discharge roller 13.

  On the other hand, after the toner image is transferred, the toner remaining on the surface without being transferred to the recording material P is removed by the cleaning blade 6a of the cleaning device 6 and used for the next image formation.

  By repeating the above operations, image formation can be performed one after another.

[2. Heat fixing device 11]
(2-1. Overview of configuration and operation)
Next, an example of the heat fixing device 11 according to the present invention will be described with reference to FIG. FIG. 2 is a cross-sectional view along the conveyance direction (arrow K direction) of the recording material P. A heat fixing device 11 shown in FIG. 2 is a pressure roller driving type fixing device using a flexible endless belt as a fixing film.

  The fixing device 11 includes a ceramic heater (hereinafter referred to as a heater) 20 as a heating body for heating toner, a fixing film 25 as a rotating body including the heater 20, and a pressure member in contact with the fixing film 25. The pressure roller 26 and the temperature controller 27 for controlling the temperature (fixing temperature) of the heater 20 are configured as main components.

  The heater 20 and the pressure roller 26 are pressed against each other with the fixing film 25 interposed therebetween to form a fixing nip portion N. When the pressure roller 26 is rotationally driven in the counterclockwise direction indicated by the arrow R26, the fixing film 25 is fixed by a rotational force acting on the fixing nip N between the pressure roller 26 and the fixing film 25. The film 25 is driven to rotate in the clockwise direction indicated by an arrow R25 while the inner surface of the film 25 slides in close contact with the downward surface of the heater 20.

  In a state where the pressure roller 26 is driven to rotate, the fixing film 25 is driven and rotated, power is supplied to the heater 20, the heater 20 is heated to a predetermined temperature, and the temperature is adjusted. A recording material P carrying an unfixed toner image T is introduced between the fixing film 25 and the pressure roller 26 in the fixing nip N, and the toner image carrying surface side of the recording material P is fixed to the fixing film 25 in the fixing nip N. The fixing nip N is nipped and conveyed together with the fixing film 25 in close contact with the outer surface. In this nipping and conveying process, the heat of the heater 20 is applied to the recording material P through the fixing film 25, and the unfixed toner image T on the recording material P is heated and pressurized on the recording material P to be melted and fixed. . The recording material P that has passed through the fixing nip N is separated from the fixing film 25 by curvature.

  Further, the fixing device 11 includes, as a temperature detection element, the surface of the recording material P that has passed through the fixing nip, including a heater temperature thermistor 21 attached to the back surface of the heater 20 in order to measure the temperature of the heater 20. A paper discharge temperature thermistor 28 for measuring the temperature (paper discharge temperature) and a pressure roller temperature thermistor 30 for measuring the surface temperature of the pressure roller 26 are provided. The temperature detected by each temperature detection element is monitored by the CPU 23.

  Hereinafter, main parts constituting the fixing device 11 will be described in detail.

(2-2. Heater 20)
The heater 20 is, for example, a ceramic heater, and is formed by forming a resistor pattern 20b on a heat-resistant substrate 20a such as alumina by printing, for example, and covering the surface with a glass layer 20c. It is long in the left-right direction perpendicular to the direction (arrow K direction), that is, longer than the width of the recording material P. The heater 20 is supported by a heater holder 22 attached to the apparatus main body M. The heater holder 22 is a member formed in a semicircular cross section with heat-resistant resin, and also acts as a guide member that guides the rotation of the next fixing film 25.

(2-3. Fixing Film 25)
The fixing film 25 is formed of a heat-resistant resin such as polyimide or a metal such as SUS in a cylindrical shape, and is loosely fitted to the heater 20 and the heater holder 22 described above. The fixing film 25 is pressed against the heater 20 by the pressure roller 26, whereby the back surface of the fixing film 25 is brought into contact with the lower surface of the heater 20. The fixing film 25 is configured to rotate in the arrow R25 direction as the recording material P is conveyed in the arrow K direction by the rotation of the pressure roller 26 in the arrow R26 direction. Note that the left and right ends of the fixing film 25 are regulated by guide portions (not shown) of the heater holder 22 so that they do not come off in the longitudinal direction of the heater 20. Further, grease is applied to the inner surface of the fixing film 25 in order to reduce sliding resistance between the heater 20 and the heater guide 22.

(2-4. Pressure roller 26)
The pressure roller 26 is provided with a heat-resistant release layer 26b having elasticity such as silicone rubber on the outer peripheral surface of a metal cored bar 26a. The fixing film is formed from below by the outer peripheral surface of the release layer 26b. 25 is pressed against the heater 20 to form a fixing nip portion N with the fixing film 25. If the width (nip width) in the rotation direction of the pressure roller 26 in the fixing nip portion N is a, the nip width a is such that the toner on the recording material P can be suitably heated and pressed. Is set.

(2-5. Temperature control unit 27)
The temperature control unit 27 includes a CPU 23 and a triac 24 as shown. The CPU 23 controls the power supply to the heater 20 by controlling the triac 24 based on the temperatures detected by the paper discharge temperature thermistor 28 and the pressure roller temperature thermistor 30, thereby adjusting the temperature of the heater 20. .

(2-6. Discharge Temperature Thermistor 28)
The discharge temperature thermistor 28 is provided in the vicinity of the downstream side of the fixing nip N with respect to the conveyance direction K of the recording material P, and measures the surface temperature of the recording material P that has passed through the fixing nip. In the present embodiment, as an example, a thermistor 28 that detects the surface temperature of the surface (printing surface in the case of single-sided printing) that contacts the fixing film 25 side of the recording material P is employed. On the fixing film 25 side of the recording material P, the thermistor 28 is a non-contact type because the toner may not be solidified immediately after passing through the fixing nip and the heat capacity of the thermistor itself can be ignored. Of course, the surface temperature of the surface (the non-printing surface in the case of single-sided printing) that contacts the pressure roller 26 side of the recording material P may be detected by changing the arrangement of the thermistor 28.

(2-7. Pressure roller temperature thermistor 30)
The pressure roller temperature thermistor 30 is disposed in the vicinity of the pressure roller 26 and measures the surface temperature of the pressure roller 26. In the present embodiment, as an example, a non-contact type thermistor 30 is employed for the pressure roller 26. Of course, a contact type thermistor may be employed.

[3. Fixing temperature correction]
(3-1. Measurement of initial pressure roller temperature Tr)
First, the pressure roller thermistor 30 measures the initial temperature Tr of the pressure roller 26 when the printer receives a print signal and starts driving (printing operation) for image formation.

(3-2. Measurement of discharge temperature Tp)
Next, after starting printing, fixing is performed at a predetermined temperature control, and the paper discharge temperature thermistor 28 measures the paper discharge temperature Tp of the recording material P after passing through the fixing nip. The measurement point of the discharge temperature Tp is not particularly limited, but the temperature of the entire system of the fixing device 11 is increased by the pre-rotation and the interval between sheets, and the temperature of the entire system is gradually deprived of heat by passing the recording material P. Since the sheet is lowered, the discharge temperature tends to decrease from the front end to the rear end of the recording material P in the transport direction. Therefore, it is preferable to measure the discharge temperature Tp at a point where the fixability is more severe.

  Therefore, in this embodiment, measurement is performed at a point of about 30 mm from the rear end of the recording material P with respect to the transport direction. Of course, the transition of the discharge temperature Tp may be measured over the entire length of the recording material P with respect to the transport direction.

(3-3. Correction of fixing temperature)
Conventionally, as described above, the fixing temperature of the subsequent recording material is corrected based only on the paper discharge temperature Tp. For example, as shown in FIG. 8, the threshold value for Tp is fixedly set at 70 ° C., and if Tp is less than 70 ° C., no correction is made. The correction is performed by lowering by 10 ° C.

  On the other hand, in the present embodiment, the fixing temperature of the subsequent recording material is corrected based on the initial pressure roller temperature Tr and the discharge temperature Tp of the recording material P. For example, as shown in FIG. 7, first, a threshold value is set for the paper discharge temperature Tp that changes according to the initial pressure roller temperature Tr. Specifically, when Tr <50 ° C., the threshold is set to 60 ° C., when 50 ° C. ≦ Tr <100 ° C., the threshold is set to 70 ° C., and when Tr ≧ 100 ° C., The threshold for the paper discharge temperature Tp is set to 80 ° C. That is, the higher the initial pressure roller temperature Tr, the higher the threshold value for the paper discharge temperature Tp. If the paper discharge temperature is lower than the threshold value, no correction is performed.

  The correction amount when correction is performed is -10 ° C., but it goes without saying that this correction amount is merely an example, and it depends on the combination of the temperature of both Tr and Tp. Different correction amounts may be set. In addition, the correction is set not to be performed when Tp is less than the threshold value, but it is needless to say that another correction may be added instead of performing no correction at all here. In short, the correction content is determined according to the comparison result between Tp and the threshold value.

  In order to improve data reliability, the discharge temperature Tp for one recording material is not used as a target to be compared with a set threshold value, but for example, the discharge of five consecutive recording materials is eliminated. The average value of the paper temperature may be used to determine the correction content of the fixing temperature for the sixth and subsequent sheets. Of course, different values may be applied to the number of sheets for which the average value is taken and the number from which the correction is applied.

(3-4. Comparative experiment with conventional example)
In order to examine the effect of this embodiment in which the correction content of the fixing temperature is set based on the initial pressure roller temperature Tr and the paper discharge temperature Tp as described above, a comparative experiment with the conventional example was performed. The comparison target is the conventional example 1 where the fixing temperature is not corrected and the fixing temperature is set with emphasis on the fixing property of the rough paper, and the conventional example 2 is corrected only from the paper discharge temperature Tp as shown in FIG. This is a case where the content is determined and the fixing temperature is corrected. The average value of five consecutive sheets was used as the paper discharge temperature Tp in Conventional Example 2 as in this embodiment.

  Here, for each of the present embodiment and the conventional examples 1 and 2, the evaluation of the fixing property of the rough paper and the curling of the thin paper was performed by changing the state of the fixing device 11 before printing. In order to change the state before printing of the fixing device 11, after 100 sheets are intermittently passed once and brought to a very high temperature state, the stop time is changed to 5 seconds stop, 5 minutes stop, 1 hour or more stop. Was evaluated. The rough paper is Fox River Bond # 24 manufactured by Fox River Paper, and the thin paper is Canon Offy Sprunner manufactured by Canon. After leaving it in an environment of 23 ° C / 50% RH for 24 hours or more, the character pattern is continuously 100 Sheets were printed and the fixability and curl were evaluated.

  The results are shown in FIG. In the figure, ○ indicates a good level, Δ indicates a level that is slightly inferior to ○, but has no practical problem, and × indicates a defective level.

  First, the conventional example 1 in which the fixing temperature is not corrected is examined. Since the conventional example 1 is a fixing temperature setting that emphasizes the fixing property, there is no problem with the fixing property of the rough paper, but 100 sheets of paper are passed through. In a high temperature state where only 5 seconds have passed since the paper, an excessive amount of heat was supplied to the toner on the recording material, causing curling of the thin paper.

  Also, the state of the fixing device 11 before printing, that is, the case where the initial pressure roller temperature Tr is low until it becomes equal to the ambient temperature as in the case where one hour or more has passed after passing 100 sheets, conversely, Tr Since the transition of the paper discharge temperature Tp during continuous printing is different from the case of a very high value, and the paper discharge temperature Tp for the same number of sheets does not necessarily match, in Conventional Example 2, the rough paper and thin paper of the recording material P are identified. Has been misdetected. For this reason, in Conventional Example 2, if the initial pressure roller temperature Tr is too low, the fixing temperature is corrected to be higher than the appropriate value, and if Tr is too high, the fixing temperature is corrected to be lower than the appropriate value. The problem of fixing quality, such as curling and rough paper fixing, occurred.

  On the other hand, in the present embodiment, in addition to the discharge temperature Tr, the state of the fixing device 11 before printing, that is, the initial pressure roller temperature Tr is also taken into consideration in advance, so that the content of correction is determined. The accuracy of discrimination power can be improved, and the problem of fixing quality due to erroneous detection can be prevented. For this reason, the present embodiment can achieve both a good level of both the fixing property of the rough paper and the curling of the thin paper regardless of the state of the fixing device 11 before printing.

(3-5. Other Examples of Measuring Method of Initial Pressure Roller Temperature Tr)
In order to simplify the configuration of the fixing device 11 and reduce the cost, as shown in FIG. 3, the pressure roller temperature thermistor 30 is not used, and the measured value at the heater temperature thermistor 21 is used instead of the pressure roller temperature Tr. May be. The measured value of the heater temperature thermistor 21 is slightly different from the pressure roller temperature directly measured by the pressure roller temperature thermistor 30 because the value is measured via the heater 20 and the fixing film 25, but the heater 20 is made of ceramic. The fixing film 25 is also thin, and both use low heat capacity products, so the temperature difference is very small and there is no problem in practical use.

(3-6. Modification Example of Fixing Temperature Correction)
In the above-described embodiment, the fixing temperature, which is a control parameter related to fixing, has been described as a correction target. However, any correction parameter other than the fixing temperature may be used as long as it is a control parameter that affects the fixing quality of the recording material. For example, the throughput of the recording material P and the conveyance speed (process speed) of the recording material P may be corrected. Here, the correction of the throughput of the recording material P is to change the timing at which the paper feed roller feeds the recording material P from the paper feed cassette without changing the transport speed (process speed), that is, paper during continuous printing. The number of prints per unit time is changed by changing the length of the interval. Further, the correction of the conveyance speed (process speed) of the recording material P means changing the speed at which the conveyance roller conveys the recording material, that is, changing the rotation speed of the motor that drives the image forming apparatus, and the number of prints per unit time. Is to change.

<Second Embodiment>
Next, as a second embodiment, another example of a fixing temperature correction method is shown in FIG. In addition, the part which has the same function as 1st Embodiment mentioned above uses the same code | symbol, and uses description.

[1. Configuration of discharge temperature thermistor 28]
The discharge temperature thermistor 28 is provided in the vicinity of the downstream side of the fixing nip N with respect to the conveyance direction K of the recording material P, and measures the surface temperature of the recording material P that has passed through the fixing nip. In the present embodiment, a contact type that detects the surface temperature of the surface of the recording material P that is in contact with the pressure roller 26 side (non-printing surface in the case of single-sided printing) is adopted, and in order to simplify the configuration, the paper is discharged. The temperature thermistor 28 is built in a paper discharge sensor 29 disposed in the vicinity of the downstream side of the fixing nip N, and has a function of detecting the presence or absence of the recording material P by contacting the non-printing surface side of the recording material P.

[2. Fixing temperature correction]
(2-1. Measurement of initial pressure roller temperature Tr)
First, the initial temperature Tr of the pressure roller 26 at the time when the printer receives a print signal and starts the printing operation is measured. The pressure roller temperature Tr is preferably measured directly on the surface of the pressure roller with a thermistor, but in the present embodiment, the measurement value with the heater temperature thermistor 21 is substituted for the simplification of the configuration and cost reduction. The measured value by the heater temperature thermistor 21 is slightly different from the actual surface temperature of the pressure roller because it passes through the heater 20 and the fixing film 25, but as described in the first embodiment, the heater 20 Is made of ceramic, and the fixing film 25 is also thin, and both use low heat capacity products, so the temperature difference is very small and there is no problem in practical use. Of course, if higher accuracy is required, a thermistor 30 dedicated to measuring the temperature of the pressure roller 26 as shown in FIG. 2 may be provided and used.

(2-2. Measurement of initial temperature Tp0 of discharge temperature thermistor)
Similar to the measurement of the initial pressure roller temperature Tr described above, the initial temperature Tp0 of the discharge temperature thermistor 28 is measured when the printer receives the print signal and starts the printing operation. As in the present embodiment, when the thermistor 28 that is a contact type and is built in the paper discharge sensor 29 is used, the paper discharge sensor 29 has a heat capacity, and therefore, depending on the state of the paper discharge sensor 29 at the start of printing. The transition of the paper discharge temperature Tp is different. Therefore, the initial temperature Tp0 of the paper discharge temperature thermistor 28 is measured in order to recognize in advance the state of the paper discharge sensor 29 at the start of printing.

(2-3. Measurement of discharge temperature Tp)
After the start of printing, fixing is performed at a predetermined temperature control, and the paper discharge temperature thermistor 28 measures the paper discharge temperature Tp of the recording material P after passing through the fixing nip. The measurement point of the paper discharge temperature Tp is not particularly limited, but in this embodiment, the contact type and the thermistor 28 built in the paper discharge sensor 29 are used, and therefore the heat capacity of the paper discharge sensor 29 is affected. The paper discharge temperature Tp detected by the thermistor 28 tends to approach the true paper discharge temperature while gradually increasing from the front end to the rear end of the recording material P with respect to the transport direction. Therefore, it is preferable to measure the paper discharge temperature Tp at a point closer to the true paper discharge temperature.

  Therefore, in this embodiment, measurement is performed at a point of about 30 mm from the rear end of the recording material P with respect to the transport direction. Of course, the transition of the discharge temperature Tp may be measured over the entire length of the recording material P with respect to the transport direction.

(2-4. Correction of fixing temperature)
In the present exemplary embodiment, as in the first exemplary embodiment, as an example, correction of the fixing temperature is performed as correction of a control parameter related to fixing. Of course, any control parameter that affects the fixing quality of the recording material may be subject to correction other than the fixing temperature. For example, the throughput of the recording material P and the conveyance speed (process speed) of the recording material P may be corrected.

  In the present embodiment, the fixing temperature of the subsequent recording material is corrected based on the initial pressure roller temperature Tr, the initial temperature Tp0 of the paper discharge temperature thermistor 28, and the paper discharge temperature Tp of the recording material P. For example, as shown in FIG. 10, first, a threshold value for the paper discharge temperature Tp corresponding to the initial pressure roller temperature Tr is set. This threshold value is not a constant value as in the first embodiment described above, but is represented by a linear function of Tp0.

  For example, when 50 ° C. ≦ Tr <100 ° C., the threshold value for the paper discharge temperature Tp is set to 0.2 × Tp 0 + 65 ° C. In FIG. 5, a straight line a indicated by a solid line is a threshold value set at this time. When the initial pressure roller temperature Tr <50 ° C., the threshold for the paper discharge temperature Tp is set to 0.2 × Tp 0 + 55 ° C. where the Tp axis intercept of the straight line a is −10, and Tr ≧ 100 In the case of ° C., the threshold value for the paper discharge temperature Tp is set to 0.2 × Tp 0 + 75 ° C. in which the Tp axis intercept of the straight line a is +10. The straight line b shown by the one-dot chain line in FIG. 5 is a threshold value set when Tr <50 ° C., and the straight line c shown by the broken line is a threshold value set when Tr ≧ 100 ° C.

  When the discharge temperature Tp is less than this threshold value, no correction is performed, and when Tp is equal to or higher than this threshold value, correction is performed to lower the heater 20 by 10 ° C.

  In the present embodiment, as in the first embodiment, in order to improve data reliability, the discharge temperature Tp for a single recording material is not used as a target to be compared with a set threshold value. The average value of the discharge temperature of the five continuous recording materials may be used to determine the correction content of the fixing temperature for the subsequent sixth and subsequent sheets. Of course, different values may be applied to the number of sheets for which the average value is taken and the number from which the correction is applied.

(2-5. Comparison experiment with the first embodiment)
In order to investigate the effect of the present embodiment in which the correction content of the fixing temperature is set in consideration of not only the initial pressure roller temperature Tr and the paper discharge temperature Tp but also the initial temperature Tp0 of the paper discharge temperature thermistor 28 as described above, A comparison experiment with the first embodiment in which the correction content of the fixing temperature is determined without considering Tp0 was performed. The content of the experiment is the same as the comparative experiment conducted in the first embodiment.

  The results are shown in FIG. As shown in FIG. 9, the first embodiment can achieve both a good level of fixing of rough paper and a curl of thin paper regardless of the state of the fixing device 11 before printing. It was not always maintained, and as shown in FIG. However, according to the present embodiment, it is possible to achieve both a good level of both the fixing property of the rough paper and the curling of the thin paper even in such a scene. In the present embodiment, when setting the correction content of the fixing temperature, it can be said that a more appropriate correction of the fixing temperature has been performed in consideration of the initial temperature Tp0 of the paper discharge temperature thermistor 28.

<Other embodiments>
The present invention has been described with the most realistic and preferred embodiment at the present time, but the present invention is not limited to the disclosed embodiment, but includes various modifications and equivalent configurations. .

  For example, the film heating type heat fixing apparatus in the above-described embodiment employs a pressure roller driving method in which a pressure roller is used as a driving roller and a fixing film is driven by frictional force with the pressure roller as a fixing film driving method. did. This is adopted because it is a low-cost configuration with a small number of parts. However, instead of this, other fixing film driving methods, for example, a method in which a driving roller is provided on the inner peripheral surface of an endless fixing film and the fixing film is driven while tension is applied, or the film is wound into a roll-end web. In addition, a method of driving this may be adopted.

  The present invention may be any heat fixing apparatus that heats an image on a recording material by nipping and conveying a recording material carrying an image at a nip between a heating member and a pressure member, as in the above-described embodiment. It is possible to adopt not only a film heating method but also a heat roller method.

  In the above-described embodiment, the heater 20 serving as a heating body for heating the toner is a ceramic heater, but is not limited thereto. For example, an electromagnetic induction heat generating member such as an iron plate may be used. By using an electromagnetic induction heat generating member such as an iron plate as a heater, this is disposed at the position of the fixing nip portion, and a high frequency magnetic field generated by an electromagnetic coil and a magnetic core as an alternating magnetic flux generating means is applied thereto. An apparatus configuration that generates heat can also be used. Moreover, it can also be set as the apparatus structure which uses the film itself as a moving member as an electromagnetic induction heat generating member, and generates heat with an alternating magnetic flux generation means.

  The present invention is not limited to a heat fixing device that heat-fixes an unfixed image as a permanent image on a recording material, but also a heating device for hypothetically attaching an unfixed image on a recording material, or a recording material carrying an image. It also includes a heating device that modifies image surface properties such as gloss by heating.

  The image forming method of the image forming apparatus is not limited to the electrophotographic method, and may be an electrostatic recording method, a magnetic recording method, or the like, or may be a transfer method or a direct method.

Claims (4)

An image forming unit for forming an unfixed toner image on a recording material;
An endless belt, a heater that contacts an inner surface of the endless belt, and a pressure roller that forms a fixing nip portion together with the heater via the endless belt, and carries an unfixed toner image at the fixing nip portion. A heating fixing unit that heats and fixes an unfixed toner image on the recording material by sandwiching and conveying the recording material to be recorded,
A temperature detecting element for detecting the temperature of the recording material that has passed through the fixing nip,
A correction means for comparing a detection temperature of the temperature detection element and a threshold value to correct a control parameter relating to fixing of a recording material carrying an unfixed toner image;
An image forming apparatus having
The threshold value is set according to the temperature of the pressure roller when the print signal is received in a standby state waiting for the print signal,
When receiving a print signal in the standby state and printing continuously on a plurality of recording materials, the correction means includes the threshold value set according to the temperature of the pressure roller, and the fixing nip portion. The control parameter relating to the fixing of the subsequent second recording material in the continuous printing is corrected by comparing the temperature detected by the temperature detection element of the first recording material that has been heated and fixed by the printer and passed through the fixing nip portion. An image forming apparatus.   The image forming apparatus according to claim 1, wherein the control parameter is a control target temperature of the heater.   The image forming apparatus according to claim 1, wherein the control parameter is a conveyance interval when a plurality of recording materials are continuously conveyed.   The image forming apparatus according to claim 1, wherein the control parameter is a conveyance speed of a recording material.

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